Several conodont taxa have been suggested for use as biostratigraphic tools in the Pennsylvanian, but each has its limitations. Some are severely restricted paleobiogeographically or paleoecologically. Others existed through a relatively short interval of time, leaving the bulk of the Pennsylvanian column unzoned. Frustratingly, the single most promising group, the Idiognathodus-Streptognathodus plexus, has eluded taxonomic treatment that is both phylogenetically sound and biostratigraphically useful.

Gondolella Stauffer and Plummer, 1932 (type-species G. elegantula, O.D.), is subject to many of these restrictions, especially geographically and paleoecologically, but offers a highly precise zonation in the rocks where it does occur that can serve as an interim standard for some (mostly Missourian) and a supplement for others (mostly Desmoinesian). Enough occurrences have been amassed to facilitate interregional, and in some cases, intercontinental correlations.

Desmoinesian gondolellids are known from 9 stratigraphic units in the Illinois basin and 5 from the Mid-Continent, and 5 zones are recognized. Distribution is relatively uniform, and zonation of this part of the column is almost total. This zonation is less detailed than the contemporary Neognathodus zonation, but it is a valuable supplement to it. The most dense concentration of Gondolella-bearing units is in the Mid-Continent Missourian where 15 units have produced gondolellids. These and the 6 Illinois basin units can be assigned to at least 6 zones, totally contiguous in the lower Missourian, less so upward. The Virgilian cannot be completely zoned, but the 2 productive Mid-Continent units are assigned to different zones.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.